Method for calibrating a packaging containers

ABSTRACT

Packaging containers for liquid contents, for example milk, are normally manufactured from laminated packaging material including a carrier or core layer of fiber material which is coated on each side with plastic layers. In order to facilitate folding of the material, this is normally provided with a pattern of weakening crease lines which facilitate the reforming into the desired packaging container configuration. A method of retroforming or calibrating a packaging container for realizing more accurate final configuration, sharper fold lines and thereby for imparting to the packaging container improved steadiness and stability comprises the steps of surrounding the packaging container (1) with a forming device (11) adapted to the final configuration of the packaging container, and of displacing parts (12, 13) of the forming device towards one another so that the free space for the packaging container is briefly reduced. An apparatus for carrying the method according to the present invention into effect comprises a forming device (11) with moving forming parts which, in the closed position, define a forming cavity of a volume which amounts to between 100 and 110 per cent of the theoretical minimum volume of a processed packaging container.

TECHNICAL FIELD

The present invention relates to a method for retroforming, orcalibrating, a sealed packaging container which is manufactured fromflexible packaging material and which contains flexible, incompressiblecontents. The present invention also relates to an apparatus forretroforming, or calibrating, sealed packaging containers filled withliquid contents and of the type which are manufactured from flexiblepackaging material.

BACKGROUND ART

It is common practice in the food industry to pack liquid contents suchas juice or milk in packaging containers of single-use disposable typewhich are manufactured from a flexible, liquid-tight packaging material.The substantially parallelepipedic packaging containers which aremarketed under the brand name Tetra Brik® are described in greaterdetail in European Patent No. EP 91712, to which reference is now made,and are thus manufactured from a flexible packaging laminate whichcomprises a carrier or core layer of fibre material, for example paper,which is coated on each side with relatively thin layers ofthermoplastic material, normally polyethylene. The packaging laminatemay also include further material layers, such as barrier layers ofmetal or other barrier materials in order to provide improved protectionagainst light or oxygen gas when particularly sensitive products are tobe packed.

In the manufacture of the above-outlined prior art packaging containers,a packing or filling machine is employed which stepwise reforms apreferably web-shaped packaging laminate into individual, filledpackaging containers. In order to facilitate the reforming process, thepackaging laminate is provided with a pattern of fold or crease lineswhich are formed by pressing of the packaging laminate between rollerswith cooperating ridges and depressions which, above all because ofsoftening of the fibre layer, impart to the material a tendency to befolded along the weakened, linear areas created in this process. Thereforming of the original, substantially cushion-shaped filled andsealed packaging containers into parallelepipedic form will hereby befacilitated. The so-called final forming above all comprisesflat-pressing, inward folding and sealing of formed corner flaps to theoutside of the packaging container, so that a substantiallyparallelepipedic configuration is achieved. Since, principally foreconomic reasons, attempts are made in the art to minimise the quantityof material included in the packaging laminate, the packaging laminateitself is relatively thin, with the result that the difference infolding tendency between the parts of the laminate provided with fold orcrease lines and the unaffected parts is relatively slight.Consequently, the reforming of the packaging laminate into packagingcontainers and, in particular the so-called final forming operation mayresult in a packaging container which not always obtains the desired,well-defined edges and corners but tends to display a more roundedtransitional area between the different wall surfaces of the packagingcontainer disposed at angles to one another. A more undefinedconfiguration further entails the disadvantage that the packagingcontainer will, in the finished state, be perceived by the consumer asmore markedly yielding and unstable, which may impede the consumer'shandling of the packaging container, primarily in connection withpouring of the contents from the container.

The method and the apparatus according to the present invention maynaturally also be employed in other, for instance prismaticconfigurations of packaging containers which are manufactured by foldingand sealing of flexible packaging material.

There is thus a general need in the art to realise a packaging containerof the above-outlined type possessing well-defined--orcalibrated--configuration and improved steadiness and stability. With aview to realising this object, attempts have been made in the art tomodify the packaging laminate by incorporating layers of differentmaterial types and properties, but this has however most generallyentailed that the packaging laminate becomes more expensive. Trials havealso been carried out with different types of crease or weakening lines,with the intention of realising a more manifest weakening of thematerial so that folding and forming are facilitated, but no tangibleimprovement has been achieved. In order to obtain a packaging containerpossessing well-defined or calibrated configuration and improvedstability, one option which has been indicated in the art is to increasethe thickness of the packaging laminate and, in particular, the fibrelayer, which naturally entails increased costs and, as a result, hasbeen put into practice to only a limited extent.

SUMMARY OF THE INVENTION

One object of the present invention is thus to realise a method ofretroforming or calibrating a packaging container which is manufacturedfrom flexible packaging material and contains preferably liquidcontents, the method making it possible to obviate the above-outlineddrawbacks and to realise a packaging container possessing considerablyimproved steadiness and stability as well as a better defined contour.

A further object of the present invention is to realise a method whichmakes it possible, by a simple and uncomplicated process, to calibrate apackaging container so that it assumes its predetermined configurationwith a high degree of accuracy.

Yet a further object of the present invention is to realise a method ofimparting to a packaging container sharp and well-defined edge lines andcorners, whereby the appearance and stability of the packaging containerare improved.

The above and other objects have been attained according to the presentinvention in that a method of the type described by way of introductionhas been given the characterizing feature that the packaging containeris surrounded by a forming device adapted to the desired final form ofthe packaging container, the forming device comprising forming partswhich are moved towards one another so that the free space available forthe packaging container is briefly reduced.

A further object of the present invention is to realise an apparatus forcalibrating sealed packaging containers which are manufactured fromflexible packaging material and are filled with liquid contents. Theapparatus according to the present invention should further be ofsimple, dependable construction and be designed so as to be able to beintegrated into existing packing machines for the production of, forexample packaging containers of the Tetra Brik® type.

Still a further object of the present invention is to realise anapparatus of the above-outlined type which is economical to manufactureand operate and at the same time makes possible the reliable finalforming or calibration of produced packaging containers.

The above and other objects have been attained according to the presentinvention in that an apparatus of the type described by way ofintroduction has been given the characterizing features that itcomprises a forming device consisting of movable forming parts which aredisplaceable between an open and a closed position in which a cavitydefined by the forming parts has a volume which amounts to between 100and 110 per cent of the theoretical minimum volume of a processedpackaging container.

The method and the apparatus as devised according to the presentinvention make for a final forming or calibration of per se knownpackaging containers, which imparts to the packaging containers aconsiderably better defined configuration and increased steadiness andstability and, as a result, improved consumer friendly handling. As aresult of the temporary volume reduction undertaken in connection withthe calibration process according to the invention, the packagingcontainer is obliged to adapt to the inner configuration of the formingdevice, with the result that, in particular along the edge lines andcorners of the container, the fibre layer of the material is given moreclearly defined folds.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Preferred embodiments of both the method and the apparatus according tothe present invention will now be described in greater detailhereinbelow, with particular reference to the accompanying schematicDrawings which show only those parts essential to an understanding ofthe present invention. In the accompanying Drawings:

FIG. 1 is a perspective view of a prior art packaging container of atype in which the present invention may reduced into practice;

FIG. 2A shows, on a larger scale, a section through a part of a per seknown packaging laminate provided with fold or crease lines;

FIG. 2B shows the packaging laminate according to FIG. 2A after folding;

FIG. 3 is a perspective view of an apparatus according to the presentinvention;

FIG. 4 shows, on a larger scale, a section through a part of theapparatus according to FIG. 3; and

FIG. 5 shows, on a larger scale, a section through a folded portion of apackaging container in which the method according to the presentinvention has been applied.

DESCRIPTION OF PREFERRED EMBODIMENT

The method and apparatus according to the present invention are intendedto be utilised for retroforming or calibrating a sealed packagingcontainer which is manufactured from flexible packaging material andcontains flexible and incompressible contents, with a view to impartingto the packaging container a better defined form with clearly marked"sharp" edge lines and corners, whereby the package is given greatersteadiness and stability and also improved appearance. The method andthe apparatus according to the present invention are describedhereinbelow applied to a prior art packaging container of theparallelepipedic type (Tetra Brik®), whose design and construction, andalso the manner of its manufacture, are disclosed in EP 91712, to whichreference is now made. The method and the apparatus may naturally beapplied to any given type of packaging container whatever, on the solecondition that the packaging material is sufficiently flexible to bephysically influenced, and that the packaging container is wholly orpartly filled with flexible and incompressible contents, for examplecontents containing a greater or lesser proportion of liquid.

A parallelepipedic packaging container 1 which has been selected for thepurposes of illustrating the method and the apparatus according to thepresent invention comprises a substantially planar top 2, a similarlyplanar bottom (not visible) and four substantially planar side panels 3disposed at right angles to one another. The packaging container 1 isproduced by the folding, severing and sealing of web-shaped, flexiblepackaging laminate and, during the forming process, a surplus ofmaterial occurs which, in a per se known manner, is flat-laid intotriangular corner flaps 4. Only one of these is visible in FIG. 1, sinceboth of the corner flaps 4 located at the top end of the packagingcontainer are, after the flat-pressing operation, folded downwards andsealed to two of the side panels 3 of the packaging container 1, whilethe packaging container's two corner flaps located at its bottom endhave been flat-laid and sealed to the bottom surface of the packagingcontainer which is not visible on the Drawing.

Like many similar packaging containers, the packaging container 1 isproduced from a laminate packaging material 5 which, in order tofacilitate folding and forming, has a number of fold or crease lines 6which are disposed in the desired pattern over the surface of thepackaging material. The fold lines 6 are realised in a per se knownmanner in that the material, prior to reforming into individualpackaging containers, is caused to pass between two rollers whichdisplay the desired linear pattern in the form of male and female parts,respectively. The packaging material 5 includes a central, relativelythick carrier or core layer 7 of fibre or paper material which is coatedon each side with relatively thin plastic layers 8, 9 of thermoplasticmaterial, preferably polyethylene. The two plastic layers 8 and 9 serve,on the one hand, as liquid-tight layers and, on the other hand, assealing material since, on reforming of the packaging laminate intoindividual packaging containers, they are utilised to make possible heatsealing of the packaging material.

FIG. 2B shows the prior art packaging material according to FIG. 2Aafter folding through 90° along the fold line 6 which, for example,corresponds to a section through one of the vertical edge lines 10 ofthe packaging container 1 shown in FIG. 1. It will be apparent from FIG.2B how the packaging material 5, after the folding operation, creates anedge line 10 possessing a relatively diffuse contour, which isintimately related partly to the structure of the core layer 7 of thepackaging material 5, and partly to the relatively undefined formingoperation which is at present employed for imparting to the packagingcontainer the desired final parallelepipedic configuration. The overlyindistinct form of the edge lines 10 has a negative effect on theappearance of the packaging container and moreover reduces thepossibility of utilising the edge lines 10 as rigidifying "beams" in thelargely flexible packaging construction.

When the method according to the present invention is put into practicein the packaging container 1 illustrated in FIG. 1, use is preferablymade of a forming device 11 of the type which is illustrated in FIG. 3.The forming device comprises a number of mutually movable forming parts,namely substantially rectangular platformed upper and lower formingparts 12a and 12b, and two side forming parts 13a and 13b which aresubstantially U-shaped in cross section. The forming parts are mutuallymovable and may be displaced from an open to a closed position(indicated by means of the arrows in FIG. 4) and vice versa. The innerdefining surfaces 14a, 14b which define the U-shape of the two sideforming parts 13a and 13b define a space which is rectangular in crosssection and whose size and form substantially correspond to the crosssectional configuration of the packaging container 1, as will bedescribed in greater detail hereinbelow. The upper and lower formingparts 12a and 12b are of such size that, on displacement in thedirection of the arrows, they may be moved towards and adapted to thespace defined by the side forming parts 13a and 13b in order thus tocompress the packaging container 1 located in the space, as will bedescribed in greater detail below. At the upper region of the formingdevice 11, there are provided a number of folding or guide members 15which are mutually movable, for example slidable or pivotal, in order onthe one hand to facilitate infeed and discharge of a packaging container1 in the forming device 11, and on the other hand to guide parts of thepackaging container 1 in connection with the calibration (fold stamping)carried out by means of the forming device 11.

FIG. 4 is a section through a corner of a side forming part 13 includedin the forming device 11 and illustrates how this displays, along itsvertical corners, a recess 16 which is in the form of a groove ofsuitable cross section, e.g. substantially circular. However, otherconfigurations are also conceivable. The recess is of a width of between1 and 4 mm and its depth amounts to between 0.4 and 1.2 times the widthof the groove. The placing of the recess 16 coincides with the foldlines 6 provided in the packaging material 5, which entails that theforming device 11 primarily displays recesses 16 along those verticalcorners in which the edge lines 10 of a packaging container 1 underprocessing are located. However, recesses 16 in the form of grooves orsurfaces of different geometric form may also be placed at other pointsin the forming device 11 if desired, in order, for example, to indicateor strengthen the packaging material around an opening region disposedin the packaging material at that part of the packaging container whichserves as the gripping area or at any other part of the packagingcontainer where the punched pattern created with the aid of the recessmay serve either as the desired rigidification and/or as a decorativepattern included in the printed artwork on the packaging container.

FIG. 5 shows a section through the packaging material 5 at a part of thevertical edge line 10 of a packaging container 1 processed in accordancewith the present invention. It will be apparent from this Drawing Figurehow the edge line 10 has, by the method according to the invention, beengiven a considerably more manifest, projecting configuration which isalso better defined and gives a "sharper" corner than is the case inprior art packaging containers (FIG. 2B). The appearance according toFIG. 5 is achieved in that, in accordance with the present invention,the packaging container--after its production in a per se known mannerand, for example filled with liquid contents and sealed--is placed inthe forming device 11 according to the invention. More precisely, thepackaging container 1 is inserted with the aid of guide rails on whichrest the corner flaps of the packaging container. The position of thepackaging container will hereby be well-defined, whereupon the innerdefining surfaces 14a, 14b of the forming parts 13a and 13b abut againstthe side panels 3 of the packaging container 1. In this position, theupper and lower forming parts 12a and 12b, respectively, are activatedand displaced in the direction of the arrows towards the top 2 andbottom, respectively, of the packaging container 1. If necessary, theparts of the packaging container 1 (for example the corner flaps locatedin the bottom which are not visible on the Drawing) are guided with theaid of the folding and guide members 15, at the same time as the upperand lower forming parts 12a and 12b, respectively are brought intoabutment against the top 2 and bottom, respectively, of the packagingcontainer 1. The upper and lower forming parts 12a and 12b are displacedtowards one another until the volume defined by the forming parts 12 and13 has been reduced to between 100 and 110 per cent of the theoretical,minimum volume which the packaging container 1 (packaging materialtogether with volume of contents) may accommodate (the lower percentagebeing in cases of packaging containers which are not entirely filledwith liquid, i.e. which also contain a given quantity of compressiblegas). On reduction of the free space for the packaging container, thepackaging material 5 is forced, by deformation of the core layer 7 andthe two outer plastic layers 8 and 9, into the recesses or grooves 16disposed in the forming device 11 so that the fold or crease lines 9 arestamped and thereby reinforced and obtain the well-defined appearancewhich is illustrated in FIG. 5. After compression of the packagingcontainer for a short period of time (typically of the order ofapproximately 1 second), the forming parts of the forming device 11 areonce again opened so that the calibrated packaging container 1 may beremoved from the forming device. By placing the forming device 11 as apart in a per se known packing and filling machine, the describedprocessing of the packaging containers may take place as a part of theproduction cycle proper without necessitating any reduction of the speedor output rate of the machine.

Both the method and the apparatus according to the present invention maybe modified in order, if necessary, further to optimise function. Incalibration of packaging containers 1 of more complex configuration thanthe illustrated, parallelepipedic configuration, or in cases when thepackaging container has an outer surface possessing a relatively highcoefficient of friction, it may be appropriate, for facilitating theforming operation, to provide the inner defining surfaces 14 of theforming device 11 with a low friction material, for example tetrafluouroethene. In order further to facilitate the movement between thepackaging material and the forming device 11, and to ensure that thepackaging material 5 is formed to the greatest possible degree followingthe contour of the recesses 16, it is also possible to vibrate theforming device 11 during the compression operation, which may beeffected by connecting the forming device 11 to a per se known vibratorapparatus. The closure together of the individual forming parts 12 and13 of the forming device 11 may possibly also take place with avibrating motion. The arrangement for guiding and displacing thedifferent parts of the forming device 11 may be of per se known type andwill not be described in greater detail in this context. Since, inpacking and filling machines of the type which manufacture, for example,the packaging container illustrated in FIG. 1, use is often made of camsurfaces and bars for obtaining the desired well-defined movements, asimilar technique may of course also be employed for obtaining thedesired pattern of movement of the different forming parts 12 and 13.Naturally, other technology such as, for example, hydraulic or pneumaticmeans may also be employed with similar results. The two folding orguide members 15 are shown but schematically and, their design may beadapted to the needs that occur in the calibration of packagingcontainers of different types. When the packaging container includesparts which are not ready-folded, for example sealing fins, corner flapsor the like, the folding and guide members 15 may be designed so thatthey, in connection with or prior to closure of the different formingparts 12, 13 of the forming device 11, execute a rotary or linearmovement in order to influence the packaging material in a directiontowards the desired final position before the final compression takesplace with the aid of the forming device 11. In those cases when heatsealing of corner flaps or sealing fins is to be carried out inconnection with the calibration operation, hot air nozzles (not shown)or other heat generating devices are also utilised prior to thecompression operation for heating the external thermoplastic layers 8and 9 of the packaging material 5 to softening temperature within thoseregions where the sealing operation is to be effected. However, thistechnique is also well-known in the art and constitutes a freelyavailable option for a person skilled in the art.

By realising the method and apparatus according to the presentinvention, an opportunity has been created for giving packagingcontainers manufactured from flexible packaging material aretroprocessing which imparts to the packaging container a well-definedconfiguration with straight, rigid contour lines with a certain reliefeffect, which not only imparts to the packaging container a neaterappearance but has also proved to considerably improve the rigidity andconsumer handling properties of the packaging container.

The present invention may be further modified without departing from thespirit and scope of the appended claims.

What is claimed is:
 1. A method of forming a sealed packaging containercomprising the steps of:a) providing a laminate comprising a fibrouscore layer coated on each side by a thin plastic layer with at least onefold line; b) filling and sealing the laminate to form a filled, sealedcontainer; c) placing the container into a free space defined by aforming device comprising at least one side forming part having a recessconstructed to define an edge line on the container; and d) bringing thelaminate of the container into abutment with the side forming part bydisplacing the side forming part toward the container thereby reducingthe free space.
 2. The method of claim 1, wherein the free space isreduced to between 100 and 110 per cent of a theoretical minimum volumeof the packaging container.
 3. The method of claim 1, wherein the sideforming parts of the forming device are vibrated in connection with thesurrounding of the packaging container.
 4. The method of claim 1,wherein the laminate is deformed into the recess.
 5. The method of claim1, wherein the laminate is brought into abutment with the side formingpart solely by displacement of the side forming part toward thecontainer.